4) Barry Allen
We know that the Man in the Iron Mask isn’t the Earth-2 Barry Allen, but he could still be a Barry from the past or future. Time travel is a very confusing thing, but The Flash does a great job of handling it, so you have to believe the show could come up with a convincing explanation both as to why Zoom has kidnapped whatever version of Barry this might be and how he’ll factor into the series moving forward.
Bear in mind that we still don’t know what happened to the Barry who travelled back to stop his younger self saving his mother, so The Flash could very well find a clever way to tie this season two story into that somehow. Confused yet? Again, time travel can be a baffling storytelling device, but provided they handle it the right way, this could be a really unique reveal.